Threshold voltage model for narrow width MOSFETs

• Published in: Solid-state electronics 1993-09, Vol.36 (9), p.1251-1260
• Main Authors: Oh, Sung-Hun, Usman, Ahmad, Sanchez, Julian J., DeMassa, Thomas A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Electronics; Exact sciences and technology; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Transistors
• ISSN: 0038-1101; 1879-2405
• DOI: 10.1016/0038-1101(93)90162-J

An analytical threshold voltage model for narrow width MOSFETs is presented. The model is based on a Fourier solution of the two-dimensional Poisson's equation for the fully recessed oxide isolation scheme. Realistic boundary conditions are used, which make this formulation more accurate than charge conservation models and applicable to different oxide isolation schemes. The present model provides an analytical closed-form expression for the threshold voltage as a function of design and process parameters such as device width, oxide isolation type, ion implantation, and substrate bias. The model requires only one fitting parameter whose sensitivity to process and design parameters is investigated. The results obtained for the fully recessed oxide isolation case are compared with numerical data, and good agreement is obtained for device widths down to 0.25 μm for uniformly doped substrates and 0.4 μm for nonuniformly doped substrates. Surface potentials and electric fields are also generated from the solutions predicted by this model. The same Fourier solution technique can be used to model different isolation schemes by changing the fitting parameter. This is demonstrated with the LOCOS and fully recessed isolation schemes. The speed and accuracy of this model make it extremely useful for CAD applications.